Millimeter waver (mmW) CMOS transceivers have attracted heightened interest in recent years, particularly in the 60-GHz band. In fact, there is currently a high demand for mmW tunable transmission lines (t-lines) that have controllable delay but fixed characteristic impedance. These applications can be very effective for use in systems requiring high download rates of about 1.6 Gb/s within the 60-GHz band. Currently, there are many challenges to mmW in CMOS technology. For example, tunable t-lines that have fixed characteristic impedance are very sensitive to switch capacitance and therefore are difficult to make using FETs.
More specifically, conventional on-chip t-line structures generally have fixed impedance and fixed delay. Usually, delay and impedance cannot be arbitrarily chosen for a given transmission line. Instead, the delay and impedance are affected by the capacitance and inductance, which vary inversely to one another based upon the distance between the signal line and the ground return line(s). As such, while it is possible to change the delay of a transmission line, changing the delay comes at the cost of increasing signal loss, changing the characteristic impedance, and/or increasing the required area (e.g., footprint) of the transmission line device.
Changing the delay of a transmission line, however, is desirable for a number of applications. For example, delay lines are utilized in signal processing operations for adjusting the time of arrival of one signal relative to that of a second signal. The delay lines may be fabricated for digital circuitry or analog circuitry, and the delay may be fixed or variable.
However, systems that utilize delays (e.g., phased-array antenna systems) suffer from the above noted drawbacks. Accordingly, there exists a need in the art to overcome the deficiencies and limitations described hereinabove.